The invention relates to combined-function appliances which satisfy residential food refrigeration and water heating requirements. The combined refrigerator-water heaters may include controls for limiting operation during times of peak electrical use.
All modern residences include separate food refrigeration and water heating appliances. Electrical energy used by the refrigerator's compressor is added as heat to surrounding space. In summer, this heat can reduce comfort and increase air conditioning costs. Winter refrigerator heat output reduces heating system operation but typically substitutes low efficiency electric resistance heat for higher efficiency gas furnace or electric heat pump output. Current nationwide U.S. data indicate that the typical new "top freezer, automatic defrost" residential refrigerator uses approximately 1000 kWh per year and discharges approximately 8 million Btu's per year into its surroundings, about 60% of the typical annual water heating requirement.
Where available, combustion fuels (natural gas, propane, and heating oil) are preferred energy sources for domestic water heating because of their lower energy costs compared to resistance electric heating. Electric heat pump water heaters, which have favorable energy efficiencies and operating costs, have not been popular due to high initial costs and poor reliability. Typical combustion water heaters, while preferred over resistance electric heaters, have center flues which contribute to high "standby" losses (energy losses which occur while the unit is idle).
For typical residential systems, only about half the heat energy consumed by the heater is delivered in hot water; the remainder becomes combustion, standby, and distribution piping losses. In homes with the water heater located remote from the kitchen in a garage or outdoor closet (for access to combustion air), up to half the typical distribution piping heat losses are attributable to the kitchen sink, which experiences many short hot water draws. Kitchen location of a non-combustion water heater can substantially reduce water heating energy consumption.
In locations with low to moderate cooling loads, the refrigerator is typically the largest residential electrical energy user. Refrigerator energy use increases with room temperature and degree of use, such that refrigerator electrical energy use is typically highest during warm summer afternoons when many electric utilities experience peak power demands. Advanced controls and thermal storage capabilities to reduce on-peak refrigerator operation would benefit electric utilities by reducing new power generation requirements.
The only routine duty required to maintain efficient operation of the conventional refrigerator is periodic cleaning of the air-cooled condenser coil, which may become clogged with dust. Discharging the refrigeration cycle heat of condensation to a water storage tank would eliminate the only user maintenance task now required to maintain operating efficiency for standard home refrigerators.
A combined refrigerator-water heater with "off-peak" controls (i.e., operationally controlled to operate during periods of relatively low electrical energy demand, such as night time hours) would benefit homeowners, builders, electric utilities, and society as a whole. Homeowners would experience substantially lower energy costs and increased safety via elimination of a major gasfired appliance; builders would benefit from elimination of a major component which occupies floor space and requires installation management; electric utilities would benefit from increased revenues and reduced on-peak loads (i.e., loads during periods of relatively high electrical energy demand such as daytime hours); and society would benefit from more efficient energy utilization and reduced global warming.
The prior art discloses many "combined appliance" concepts which combine water heating with space heating or cooling functions. For example, U.S. Pat. Nos. 4,448,037, 4,514,990, 4,299,098, and 4,098,092 each disclose systems which provide space conditioning and water heating from a single appliance. U.S. Pat. No. 3,935,899 discloses a single heat pump connected to a plurality of hot and cold appliances located throughout a household, but without description of specific refrigeration or water heating technologies, and without considering combination of the two in a single appliance. U.S. Pat. Nos. 3,888,303 and 4,188,794 disclose multiple kitchen appliances linked by a circulating thermal exchange fluid, again without specifically disclosing a combined refrigerator water heater appliance. U.S. Pat. No. 4,821,530 discloses a refrigerator with built-in air conditioner, using two compressors and a water-cooled condenser but no use or storage of the heated water.
The prior art references do not describe a "single package," single compressor appliance which directly transfers heat to water at the condenser, capable of satisfying full refrigeration and water heating demands, with controls to limit on-peak electrical energy use; nor do they describe other more advanced combined refrigerator-water heater concepts which provide space cooling performance when refrigerator cooling loads are satisfied, and increased efficiency using multiple refrigeration systems.